The invention relates to a temperature-sensitive switch with a casing having a pot-shaped lower part and a top part, whereby in the lower part is arranged a bimetallic disk and under the action of the latter at least one movable contact part can be brought into contact with a stationary opposite contact, so that an electrical connection can be formed between the lower part, movable contact part and opposite contact.
Numerous different constructions of such miniature temperature-sensitive switches have been proposed in, for example, DE-OS Nos. 17 90 103, 21 21 802, 24 33 901, 24 42 090, 24 42 397, 25 05 966, 25 11 314, 26 44 411, 29 17 482, 31 22 899. Reference should be made thereto for further details and the content thereof forms part of the present disclosure. They are very small compact switches with a casing and a pot-shaped lower part and an upper part closing the latter, with the casing containing a switch mechanism, which has one or more contacts centrally carried and switched by a bimetallic disk. A temperature-sensitive switch to which the present invention relates has dimensions of a few millimeters, e.g. a diameter of 5 to 8 mm and a height of less than 5 mm. If there is only one contact pair including a movable contact part and a stationary opposite contact part in the simplest form the current can flow over the bimetallic disk, but preferably takes place over an additional spring snap disk to the pot-shaped casing. In the case of two movable contacts with a corresponding opposite contact, they are carried by a common support part moved by the bimetallic disk and there is a direct current flow. From the opposite contacts, which are generally arranged on the fixed part, the current can be tapped by a current transmission element on one or more outer connecting contacts. Temperature switches, namely thermostats are known, which only interrupt the electrical contact and, for restoring the electrical connection, can either be switched back manually, or can be replaced. Temperature-sensitive switches are known, which switch back automatically after a significant temperature change and restore the electrical connection. It can occur that after cooling of the bimetallic disk, the latter switches back again and restores the electrical connection without removing the fault, which has led to the separation of the electrical connection through the bimetallic disk either directly due to increased current flow or indirectly due to increased temperature development. This gives so-called regulator cycles.
It is known in connection with open switches of another type to arrange high-value resistors between the connection ends and parallel to the switching contact and through same, after opening the switch, flows a small current which produces heat, so that the bimetallic disk is held at a higher temperature and consequently keeps the switch open. The current flow is only interrupted by an external interruption of the power supply, such as through switching off a master switch, so that only then can the bimetallic disk jump back again.
The aim underlying the present invention essentially resides in constructing the aforementioned miniature temperature-sensitive switches as self-holding temperature-sensitive switches. The small dimensions of the switches and the arrangement thereof in a closed, small casing are to be retained and a more effective heat production is to be obtained for reliably keeping the switch open.
According to the invention the above aim is attended in the case of a temperature-sensitive switch with a casing having a pot-shaped lower part and a top part, whereby in the lower part is arranged a bimetallic disk and under the action of the latter at least one movable contact part can be brought into connection with a stationary opposite contact, so that an electrical connection can be produced between the lower part, and movable contact part and the opposite contact, in that between the opposite contact part and the lower part there is a permanent higher-value electrical connection through a resistor part.
For the optimum solution, the present invention does not bridge by a high-value resistor the external connecting contacts which are connected to leads, as happens in known open switches in order to give them a self-holding construction. In the case of the inventive miniature switches, this would lead to a considerable increase in the size of the complete assembly, so that it would not be possible to use them for the intended purposes. It would also be disadvantageous in such a construction that the heat transfer from the high-value resistor to the bimetallic disk would be extremely poor. Therefore, the invention proposes an integrated solution with an integrated construction of the high-value resistor in the existing casing.
According to a preferred construction, the resistor part is a PTC element. The use of such PTC elements for bridging purposes is known per se. According to a particularly preferred construction, the electrical resistance of the resistor part is adjustable. Thus, a single high-value resistor part can be used for different switches which, in the case of the same construction, have bimetallic disks with different switching temperatures, which is adjusted in accordance with the bimetallic disk used and its switching temperature and is adapted thereto. According to a preferred construction the resistor part is a metallic or carbon resistor part guided in rounded manner and, in particular, the resistor part can be stamped from a metal disk or the carbon resistor is applied as a coating to a carrier, in particular by pressing on and is covered by a solidified glass melt. For setting purposes, according to a particularly preferred construction, between individual portions of the resistor part there are removable bridges.
Thus, according to a preferred construction, the invention proposes that the previous exclusively insulating cover part, which forms a mechanical connection between the stationary opposite contact or the current transfer element connected thereto from the stationary opposite contact to an external connecting contact part and the casing lower part, is constructed as a high-value resistor element or is provided with the same, so that there is a high-value connection between the stationary opposite contact and the metallic casing lower part.
The inventive switch can in particular be used at difficultly accessible points, where there is little space and/or contamination is likely. It can therefore be used within windings of electric motors, but also in the case of pressure can be inserted in front of lamps and in heating appliances. A particular advantage results from the combination of encapsulated miniature construction and self-holding, in that the switch can replace manually resettable switches. This is because it is possible to reduce the relatively large dimensions required for the resetting device and for the same security by the inventive switch.
Further advantages and features of the invention can be gathered from the claims and description of two embodiments of the inventive temperature-sensitive switch with reference to the accompanying drawings.